Capillary tubes whose inner surface has total reflecting properties with regard to electromagnetic radiation and whose longitudinal section is substantially elliptical/part elliptical or parabolic/part parabolic, can be used for focusing and or concentration of X-ray radiation beams, so that these are concentrated to a small area with high intensity.
However, a very high surface quality is required on the inside of the capillary tube, to enable for the X-ray radiation beam to pass by means of reflection from one opening at one end of the ellipsoid to an opening at the opposite end of the ellipsoid. It has also been shown that there should be a relationship in the magnitude of 1:1000 between both axes of the ellipsoid, to achieve an advantageous focusing of the X-ray radiation beam.